In the best of times, the Costner family relies on a team of four experts to take care of 12-year-old Elizabeth, who has a severely debilitating genetic condition that makes her especially vulnerable to infection.

But now Misty Costner, the girl’s mother, is waiting to find out whether she has tested positive for the coronavirus.

She is quarantined upstairs in their small home in Arlington to avoid passing the possible infection to Elizabeth. The girl’s paid caregivers must stay away also. So Harry Costner is on his own.

“When that gets stripped away, everything gets pretty dire pretty fast,” he said in a phone interview, his little girl squealing in the background. “She’s an awesome, loving, jumping, wild girl, but it’s a lot to do for one person.”

The coronavirus pandemic that has shut down much of the nation has brought another layer of physical risk and mental anguish to the already stressed lives of people who are immunocompromised, and presents new challenges for their care providers.

Such individuals’ underlying medical conditions, or the drugs they are taking to suppress their immune systems and manage their illnesses, make them more susceptible to contracting the virus and more likely to face complications, experts said.

The category includes cancer patients undergoing chemotherapy, people with untreated HIV, and those with chronic lung, liver or kidney disease, said Clifton Bingham, a physician, professor of medicine and director of the Johns Hopkins Arthritis Center.

To varying degrees, people with rheumatoid arthritis — an autoimmune disease that affects 1 percent of the population — lupus, multiple sclerosis, inflammatory bowel disease and even psoriasis could also be at higher risk, Bingham said. Age itself is a risk factor.

Many immunocompromised individuals are practicing extreme versions of the hand hygiene, social distancing and symptom monitoring recommended for the general population.

Thomas Alfano, 62, who has a genetic primary immunodeficiency disorder, and his wife, a primary-care physician named Yasmin Panahy, increased their already meticulous germ-control regimen about three weeks ago, fearful that her work would bring her into contact with covid-19 patients.

She returns to their Bethesda home wearing a mask and gloves and takes a shower right away. Her work clothes go into a special bag for cleaning, and she emerges wearing fresh clothes and a different mask.

They stay six to 10 feet apart at all times and decontaminate their mail using medical-grade wipes. Otherwise, he’s cloistered in his 25-year-old son’s old bedroom; she’s got the master.

“We have actual walls and virtual walls,” Alfano said. “If she gets anywhere near me, I just back away or tell her ‘Back up.’ We’re very careful about it because the downside is so dramatic.”

Panahy considered moving out until the threat abates, but that option seemed too expensive, Alfano said. He’s so worried that the virus could kill him that he told his son, who lives in Germany, not to fly home for a funeral.

“For us, it’s all about mitigating the risk,” Alfano said. “If I get it, I just don’t have anything to fight it with. I’m not quite ready to go out.”

When the coronavirus hit New York in early March, Rick Mis­kovsky, a 59-year-old retired mail carrier who was treated last year for advanced kidney cancer, got strict orders from his doctor to stay home and avoid most people.

The doctor was worried that Miskovsky’s compromised immune system would make him easy prey.

“I’ve kept you alive a year and a half, and I’ll be damned if I’m going to let the coronavirus kill you,” his oncologist, Charles Drake of the New York-Presbyterian/Columbia University Medical Center, told him.

Miskovsky’s weakened defenses, unlike those of many cancer patients, did not result from chemotherapy, which drives down the number of infection-fighting white blood cells.

Rather, he had been treated with an immunotherapy drug that unleashes the immune system to attack cancer. The drug threw his system into overdrive, wiping out the cancer but also causing crippling rheumatoid arthritis. To tamp down the immune response, Miskovsky now takes Humira, which makes him vulnerable to infections.

He is under a kind of medical house arrest at his home in Queens.

“The doctor doesn’t even want him walking around the block,” said his wife, Mary.

Rick missed their nephew’s wedding, which was held before such gatherings were banned, and members of his immediate family who went sat far from the other guests to avoid picking up something to take home.

“We told the groom, ‘We can’t kiss you,’ ” Mary said.

Rick Shaub, 64, of Colorado found himself in a similar predicament in early March.

Already battling kidney cancer, he was diagnosed with myelodysplastic syndrome, a kind of blood cancer, on March 1, after undergoing follow-up medical tests at UT Southwestern Medical Center in Dallas.

Doctors decided he should receive intensive chemotherapy treatments in Dallas, but wanted him to find an isolated place to stay between sessions.

The former car dealer and his wife, Katie, relocated from their extended-stay hotel to an Airbnb farmhouse almost an hour’s drive from the hospital.

They drive back and forth several times a week for blood transfusions and chemo.

One advantage to the remote location: “I can go out, and ride my bike up and down the dirt road,” Schaub said. And he can walk his dog, a border collie that was “kind of hyper in the hotel.”

The scarcity of tests, and lag time between testing and results, has injected uncertainty into the carefully honed routines of immunocompromised individuals and their families.

The Costners, in Arlington, are still waiting for the results of Misty’s coronavirus test, which she underwent at a drive-through site at Virginia Hospital Center last Wednesday after being turned down at the hospital’s emergency room four days earlier.

She was told it could take seven business days for the swabs to be processed.

Elizabeth is deaf, blind and nonverbal, and can’t feed or clothe herself. She has lots of digestive issues, a sleep disorder and other challenges, meaning Harry Costner is on duty round-the-clock. With bad headaches, nausea, fever and cough, Misty is in “survival mode” upstairs, her husband said.

When the weather is nice, other caregivers can meet Elizabeth in the backyard, where she can jump on the trampoline and he can shower or just try to get hold of himself.

He said he is running on adrenaline, with his “fight or flight” response “stuck on the on position but jammed harder than it ever has,” exacerbating the physical and mental fatigue.

“This is the biggest hurdle I’ve faced in my life.”

Steve Klein, 55, of Bethesda understands that feeling. He tested positive for the novel coronavirus on March 19 and immediately self-isolated to protect his 18-year-old son, a college freshman who is immunocompromised and has moved home.

Even before the coronavirus hit the United States, the Klein family carried hand sanitizer, washed their hands after handling restaurant menus and rubbed down airplane seats with alcohol wipes — the habits of those who know what infection could mean for a loved one.

When the pandemic descended, they stopped eating out or ordering in. Grocery store trips happened late at night only.

Now for more than a week, Klein has seen his housemates — his wife, son and daughter — only via FaceTime.

Meals are left at the top of the stairs while he holes up in the bedroom of another son, who is grown and living elsewhere.

“It feels scary because you’re alone,” he said. “It’s been a major burden on my wife.”

When he is energetic enough, he said, he thinks about what he will do when his fever, muscle pains and migraines finally abate and he is confirmed virus-free.

“Hug my wife and kids,” he said. “Nothing beyond that, really. Hug my wife and kids.”